I grow heterodoxa, minor and nutans. I don't find them particularly difficult to grow but they do need very humid and cool conditions. Mine are grown in a closed terrarium with 80%+ humidity. Air circulation in my set up is minimal and while this situation may not be optimal, my plants don't seem to suffer for it and I've never had a problem with fungi. If you can provide air circulation without sacrificing humidity by all means do so. They like cool temperatures especially at night, along the same lines as highland Nepenthes. Most of the heterodoxa and minor in cultivation come from lowland locations so they're probably more warmth tolerant (IME both species will also tolerate temps down to 32F at night). I grow them in sphagnum and I don't sit them in water. They can sulk after root disturbance and particularly after division so take care when repotting. I find heterodoxa the most forgiving so it's probably a good one to start with.
HTH
Andrew

how low do i need to get the temperature down to and how do you do that?

My heliamphora terrarium is outside in a ~zone 9 climate so temperatures take care of themselves. From what I've read you're looking at a drop to below about 60F for good growth. Maybe others who grow highland Neps indoors can give you an idea how they do that. Maybe this is why they're considerd hard to grow.

A few years back Triffid Park had some info on their website saying they grew nutans and heterodoxa in both their hothouse and unheated greenhouse and while growth was noticeably slower in the hothouse, the plants were still healthy. While they may or may not thrive in a warm indoor terrarium those species should still survive.

how would i make the temperature drop to 60 degrees from 70 degrees if i were to grow it in a terrarium?

Open Window Maniac,

Small cooling units, a window mounted air conditioner aimed at the terrarium side (with the terrarium closed of course), watering them a little each night with cool water, or my favorite, ice water bottles set near the plants. The most costly yet easiest would be a window mounted air conditioner or small cooling unit attached to the terrarium.